Telegraph synchronizers



F. D. BIGGAM ETAL 3,033,928

TELEGRAPH sYNcHRoNIzERs 5 Sheets-Sheet l May 8, 1962 Filed Dec. 18, 1959mw mw B 8m .\moN\Nom my l 3 Nv v May 8, 1962 F. D. BIGGAM ET'AL3,033,928

TELEGRAPH SYNCHRONIZERS 5 Sheets-Sheet 2 Filed Deo. 18, 1959 A CHANNELcLocK E SDW un? PLN mx SGF. man Tm. m .J VDT mKR FR 2 m F AT RNEY May 8,1962 F. D. BIGGAM ETAL 3,033,928

TELEGRAPH sYNcHRoNIzERs Filed Dec. 18, 1959 5 Sheets-Sheet 5 2O PULSELAG INPUT 82 85 22 al e5 INVENTORS FRANK D. BIGGAM ROBERT J. REEK AVTNEY May 8, 1962 F. D. BIGGAM TAL 3,033,928

TELEGRAPH SYNCHRONIZERS Filed Dec. 18, 1959 5 Sheets-Sheet 4 DIVIDER l 2BINARY DIVIDER l 2 el |86 FIG. 5

A CHANNEL cLocK v FIG 4 NvENToRs f FRANK D. BIGGAM ROBERT J. REI-:K

BY AT TORY May 8, 1962 F. D. BIGGAM ETAL 3,033,928

TELEGRAPH SYNCHRONIZERS Filed Dec. 18, 1959 5 Sheets-Sheet 5 6v. LEVELSENSING RETARD RETARD uNIvIBRAToR FLIP-FLOP }o|scHARGE ./25l

ADVANCE ADVANCE umvxsRAToR Fup FLop W +6v. LEVEL SENSING BINARY 2 32|cRYsTAL OSC.

Lazo

BY ATToR EY Unite States 3,033,928 Y TELEGRAPH SYN CHRONIZERS Frank- D.Biggam, Chicago, and Robert J. Reek, Mount Prospect, lll., assignors toTeletype Corporation, Chicago, Ill., a corporation qi Delaware v u FiledDec. 18, 1959, Ser. No. 860,531

11 Claims. (Cl. 178--69.5) Y

This invention relates to telegraph synchronizers, and more particularlytov apparatus for synchronizing the receiving distributors in telegraphreceivers with the signals received from telegraph transmitters.

Two principal problems areinvolvedv in synchronizing the receivingdistributor, the device which places received telegraph signals into aform usable byv telegraph terminal equipment, of a synchronoustelegraph' receiver, such as a multiplex receiver.

The first problem, which may be called phase shift, arises from the factthat the positive to negative transitions' of the received telegraphsignals may vary, due to transmission losses, inrelation to a standardor optimum time detenninedfby the local time'base generator that drivesthe receiver, and hence the received signals are said to lead or lagrelative to the time base generator. This phase shift arises whenthetelegraph signals are transmitted over either wire or radio circuits.However, the problem is accentuated when the signals are transmittedover radio circuits due to` so-called multipath transmission. This typeVof transmission is caused by the radio waves, which are reflected fromthe ionosphere, and since this layer varies in height during the courseof a day, the problem iscompounded. Consequently, a particulartransition in a telegraph signal may be received directly from thetransmitter, and the same transition may be received at a laterand'varying time because of this recction from the ionosphere. If thereceiver is receiving only reected' signals, the transitions in thesignals may occur either before or after the expected time -as predictedby the time base; However, over a given period of time, such variationon either side of a given time will average out and for all practicalpurposes, the number of transitions which occur before their correcttime will equal the number of transitions which occur after such time.

An object of this invention is to provide new and imf proved apparatusfor synchronizing the distributor of la telegraph receiver with receivedtelegraph signals.

Another object of the invention is to provide new and improved telegraphsynchronizer which averages out the overall' effect of multipathtransmissions of the telegraph signals.

A feature of the invention is the provision of means for sensing leadingor lagging transitions of received telegraph signals relative to pulsesgenerated by la time base generator and means operable upon theAindication of a leading or lagging condition to subtract or add a pulseto the train of pulses supplied -by the time base generator todn've thereceiving distributor.

Another feature of the invention is the provision of means for analyzingreceived telegraph signals to determine if the transitions therein varyfrom a standard or optimum point in time.

In. accordance with one embodiment of the invention, a univibrator isemployed to control a constant current source to place a charge on alarge capacitor. If the given transitions lag the optimum time, anincremental charge of one polarity is applied to the capacitor from theconstant current source, and if the transition leads the optimum time,an incremental charge of the opposite polarity is applied to thecapacitor. charge on the capacitor will be the resultant of small,discrete steps of potential which are either positive or negative, inaccordance with the leading or lagging of the Consequently, the

, 3,033,928 Patented May 8, 1952V actual transitions in the incomingsignal with respect to an optimum time. Onthe basis that s'u'ch leadingor lagging' transitions resulting from multipath transmission willaverage out, theleading or the lagging of the actual transitions mustpersistV untily a predetermined charge of one polarityv or another' isaccumulated on the capacitor in order to initiate corrective action.Such corrective action may include either the addition or thesubtraction of drive pulses to the receiving distributor in orderto'speed up or slow down the rate of the receiver. In this manne-ri, thereceiver is maintained in synchronism with the transmitter of thetelegraph signals, a-ndthe-elec't of multipath transmission on thetransmitted signal is nullified.`

The second problem involved in synchronizing a telegraph receiver, whichmay be called Y frequencyv drift, arises from the fact that when acrystalcontrolled local oscillator is employed to generate the timebase, the natural frequency of the crystal may vary due to changes intemperature, etc, Y

Accordingly, a still further object of the invention is to V,provide newand improved 'apparatus for varying the frequency of the localoscillator of a telegraph receiver in accordance -With detected leadingandY lagging phase relations between the locally produced signals andthe Lreceived signals.

Another feature of the invention is the provision of means for varyingla variable capacitor inthe tank circuit ofv the local oscillator inaccordance with detected leadvention provides for the derivation of twoseparate and distinct controls from-'the detector of lagging or' leadingconditions of the signal transitions., One of these-controls is applieddirectly to the oscillator to vary its fre quency and, in the case of acrystal controlled oscillator, to compensate forfrequency drift due tosuch causes as temperature changes. The 'other or rephasing control isimposed upon a gating circuit that controls the application of pulsesfrom the oscillator to the receiving distributor. exceeds considerablythe number required to operate the distributor at the proper speed, andin normal operation pulses are periodically gated through to thedistributor, intervening pulses being suppressed. The' repliasingcontrol is exercised by .gating or suppressing additional pulsesto'correspondingly advance or'retard the distributor.

- Other objects and the many attendant aduantagesof the inventiongwillbecome apparent upon reference to the following description when takenin conjunctiony with the accompanying drawings in which: g

BIG. 1 is a` block diagram of a'telegraph'synchronizer embodying certainfeatures of the invention;

. FIGS; 2 to 4, inclusive, when arranged" as depicted in FIG. 5, show inschematic form the details of the circuit represented in block diagramin FlG. l;

FIG. 6 shows a plurality of waveforms of potentials Y' which appear atvdierent FIGS, 2 to 4; inclusive;

FIG. 7 is a block diagram of an alternate embodiment of the invention;and y FIG. 8 is a circuit diagram, partly schematic, showing thefrequency synchronizer for the local oscillator.

points inthe circuit shown in General Description Referring now to theblockdiagram shown in FIG. l, an incoming multiplex signal is applied toinput leads 10-10, and the incoming multiplex signal may include signalswhich are associated with four channels in a multipleX receiver. Suchchannels are usually designated as A, B, C and D.- The multiplex signalsare applied through an input relay 11 andv to a gating circuit 12 towhich is also applied a so-called clock pulse associated The oscillatorgenerates pulses at a rate which with one of the multiplex channels. Forexample, there is applied to a lead a potential condition which isdesignatedin FIG. las the A channel clock. This means that during theoperation of the A channel in Ythe multiplex receiver, a conditioningpotential is applied tothe lead 1S and to the gating circuit 12 so thatany signals which appear on the incoming leads 10a-10 pass through theVgating circuit 12. `It is theselsign/als which are used to causesynchronism of the receiver with the transmitter of the Vincomingmultiplex signals'. 0 t

Any .signals which pass through the gating circuit 12 Y are appliedthrough a pulse Shaper circuit 16 to two further Vgating circuits 20 and2.1. Connected to the gatlng y' circuits 20 and 21 are the outputs fromstages of a frequencydivider in the Vdistributor Vdriving means 'of4 thev-multiplecreceiver. In this respect, similar structure can ,be providedas disclosed in PatentNo. 2,865,996 .to T. A. Hansen, granted=December23, 1958. For this reason, `the HansenV patent isrincorporated byreference to the same extent as if it were reproduced herein initsentirety.

As shown in that patent, three stages 101i: to 10M are connected tothree gating circuits 131 vto 133, inclusive and respectively. Likewise,three further stages 4,101e to 101g of the frequency divider 101 areconnected to .three -gating circuits 141 to143, inclusive andrespectively. As disclosed "in the Hansen patient, if Va transition.occurs during the time that the stage 101er of the frequency di- Gvider 101 is operating,Y no Vcorrective'action lis taken to synchronizethe receiver with the transmitter. However,v

ifa'transition inthe incoming signal occurs before it Vin synchronismwith the received signal.

It can be seen from the above commentary that 1f, in the synchronizerdisclosed in the Hansen patent, a given Ytransition occurs during aparticular one-seventh of an impulse, the time that the stage 10h: ofthe distributor 101 is operating, no correctiveaction is taken. Thisstructure is modified in the present invention so that the outputs ofthe four stages similar to the stages 10111 to -101d,

inclusive, of the distributor 101 are connected together and'through anamplifier 22 to thegating circuirt720.

,fAlso, outputs from stages similar to the stages`101e to 101g,inclusive, are connected together and through an aosaaask y appliedthrough the amplifier fand to the gating circuit 21 energizes an advanceunivibrator 31 so that an `output from this latter univibrator energizesa constant current circuit 32to charge the capacitor 30 with a pulse ofpredetermined length and positive polarity. If, because of multipathtransmission, the gating circuits 20 and 21 are operated alternatelyforless than a predetermined time, the charge on the capacitor willmerely alternate inrnegative and positivedirections. It, however, Vanoutput from, for example, the gating circuit 20 persists for apredetermined time, say 20 seconds, sui- Y 4Q which energiz'es a gatingcircuit 41. The gating cir- VVcuit 41 is an and gate and is lsimilar infunction to the gatingcircuit including the diodes V68, 59, 73 and 74fsh'own inFIG.k 5 of the Hansen patent. Also, -as shown in the Hansenpatent, an output from a binary is applied to the gating circuit 41,Vand such a binary is similar to the binary 149 shown in FIG.5 of theHansen patent.

The application vof these pulses to the andgating circuit 41 energizesan or gating circuit 42 to actuate anisolating stage 4S and be appliedovera lead v46 to a trequency divider in the distributor driving means.As in the Hansen patent, theoutput from the isolating stage 4'5 would beapplied lto thetreqnency divider 67 s o that a pulse would be subtractedfrom the distributor-driving means to slow down theoperation of thisdistributor.

Since this structure wasV actuated'becausera transition in Y theincoming signal occurredafter it was due, it can be amplifier 25 to thegating circuit 21. With this structure,

it is assumed that a transitionin an incoming signal occurs at itsoptimum time if it occurs as the stage 101d is'being extinguished andthestage 101e is being rendered conductive. As will be discussedmorefullyherein below, should a transition occur before this time, a pulse willbe applied to the gating circuit 20, and if it occurs after this optimumtime, a pulsewill besent tothe gating circuit 21.

Any pulse resulting from a signal transition occurring and each pulsebeing applied thereto will place the univibrator in its unstable statefor a predetermined period of time. Consequently, each pulse beingapplied to the input thereof causes, at the output, a-pulse or" pre-Vdetermined length which operates a constant current cirto Vplace apredetermined, incremental and negative` charge thereon. In a likemanner, any pulse which is Vat'ter it is due and which is impressed onthe gating cir-Y A cuit 20 is applied therethrough and to a retardunivibrator Y l26. The retard univibrator 26 is a moncstable flip-flop,

seen that the Vdistributor driving Vmeans properly slowed down theoperation of the distributor so that synchronisrn of the yreceiver andtheincoming signals would be realized. Also, a second output from theretard ip-op 37 is applied to a retard discharge circuit 47 to cause areduction in the negative charge on the capacitor 30 ya will bedescribed more fully herein below. a

To. complete the description of the structure shown in block form inFIG. l, assume Vthat a transition in the incoming signal leads thedistributor in the multiplex receiver. Inthis case the leadingtransition will be ap` plied to the gating circuit 21 at the same timean output from theY ampliiier 25 is applied thereto. Consequently,

anY output from the gating circuit 21 will energize the Vadvanceunivibrator 31 to operate theconstant current -ewillrbe derivedtherefrom and inverted by a phase inverter 52, and an advance flip-flop55 will be energized thereby. vAn output fromthe advance dip-dop 5S will'operate an add univibrator 56, be appliedvto an and gating circuit 57-to Which'is also applied the output of a binary (similar to the binary189 shown in FIG. 5 of the Hansen patent, and KVthelor gating circuit 42will be operated to cause theV addition of a, driving pulse in thedistributor-driving meansof the receiver in the manner described in thevHansen patent. Also, when the advance tlip-op 55 is energized, anIoutput is derived therefrom and applied'to an advance discharge circuit60 which causes a reduction in the positive charge on the capacitor 30.VAs .will be'described more fully herein below, the potential togvvhichVthe advance discharge 'circuit places theV capacitor 30 `deterrnilltesthe maximum rate at which pulses are added to the distribi utor-drivingcircuits.

Preferred Embodimezit Referring now to the circuit diagram shown inFIGS.

be subtracted from the distributor driving means so that the distributorwill be slowed down to maintain synchronism with the incomingtrsignals.Such signals are apvplied across the input leads -10 (FIG. 2) totheinput relay' 11. The input relay 11 may be similarto a transistor relaydisclosed in a patent of Phillip G: Wray,

No. 2,905,835, issued September 22, 1959, and the disclosure of thatpatent is incorporated herein by reference 'as if it had beenreproduced` herein in its entirety. For the purposes of the presentinvention, it is suicient to state that a marking condition appearingonV the input leadsl 16-10 will cause an oscillator 61 in the line relay11 to oscillate, andsuch oscillation will continue for the time that themarking condition exists'. Also, the potential appearing on thecollector of a transistor 62 in the circuit of the oscillator 61is aninverted version Vof the signal being applied to the' input leads143-10. This inverted signal is demodulated by a demodulator 65 (alsodescribed in the Wray'patent and applied to the base of a transistor 66.The transistor 66 again inverts the sig- -4 nal being applied to thebase thereof, so that the waveform of the 'potential on the collector ofthe transistor 66 is similar to the multiplex signal being applied totheV input leads 10-10.

The output at the collector of the transistor 66 is api plied lto thegating circuit 12, to which is also applied a clock pulse from the Achannel over the lead 15. As described inthe Hansen patent, assumingthat there are four channels in the receiving multiplex equipment, eachof these channels will be allotted an equal time for receiving thesignals designated therefor. During the time that one of the channels,the A channel, is operating, a relatively-positive potential is appliedto the lead and to the right-hand side of a diode 67 in the gatingcircuit 12. This relative-positive potential, of itself, is insufficientto render the diode 67 conductive. However, when a potential similar toa marking potential appears on the collector of the transistor 66, thispositive-going transition is diierentiated by a capacitor 70 and aresistor 71 in the gating circuit 1'2. This additionalpositivespike issuiiicient to render the diode 67 conductive and will be impressedthrough a capacitor 72 to the base of a transistor 75 in the pulseShaper 16. The base of the transistor 7S is normally clamped at asufficiently-negative potential through a diode 76 to prevent theconduction thereof. When Aa positive potential spike is applied to thecapacitor 72, the transistor 75 is rendered conductive, and the positivespike will appear on the emitter thereof. This positive spike is thenapplied over leads 77 and 8?VA to the gating circuits 20 and 21,respectively.

The amplier'ZZ is a transistor as shown in FIG. 3, and the emitterthereof is connected to the gating circuit 20. As described hereinabove,output from stages similar to the-stages `lilla to lilld, inclusive, inFIG. 2 of the Hansen patent are applied to the base of the anipliiier22. Since it was assumed 4that a transition in the incoming signaloccurred before it was theoretically due, this signal will occursometime during the period that the stages lilla to 101d, inclusive, isconducting. Assuming that the output from these stages is arelatively-positive potential, this potential will be applied to thebase of the amplifier 22, will appear on the emitter thereof and will beapplied to a diode 81 in the gating circuit 20, rendering this diodenonconductive; Then, when a positivepulse is impressed on the lead 77from the emitterA of duration-of the pulse.

, 6 the transistor 75, a diode V82 is likewise rendered nonconductive.Consequently, the potential of a junction point 85 increases, andtheincreased potential thereof renders a diode `86 conductive and isimpressed throu-gh a capacitor S7 to the base of aleft-handfnormally-conducting transistor 90 and the retard univibrator26; This positive potential will. render the transistor 90-nonconductive, and since the univibrator 26 is connected as a monostableflip-flop, the transistor90 will remain nonconductive and a transistor91 associated therewith will conduct for a' predetermined time, .afterwhich the transistors 90 and 91 will revert to theI condition shown' inFIG. 3.

An output is taken from the retard univibrator 269' from the collectorof the: transistor 91,. When this' transistor was renderedconductive,"the collector potential thereof increases, andtthisincreased potential exists for the time that thernonosta-ble Illip-ilopis in its unstable condition. Consequently,I a positive pulse ofpredetermined width, say four milliseconds, is applied over a lead 92and through a capacitor 95`to the -base of a normally nonconductingtransistor `96 in the constant current circuit 27. The transistor 96functions asa switch with the emitter thereof connected throughresistors 97 and- 106 and the base connected through a resistor 1011 toa source of negative potential. For all practicalpurposes,

`the transistor 96 will be in its nonconductive conditionr when no othersignal is applied to its base.' The positive, four-'millisecond pulsefrom the collector of the transistor 91 renders the transistor 96conductive for the With the transistor 96 conductive, there is currentflow 'from ground, through a meter 'movement 102, a resistor 105, a lead106, the collectoremitterjcircuit of the transistor 90, and theresistors 9-7 Aand to the negative source of potential. This currentilowproduces a negative voltage at the junction of the resistor 10S and thecapacitor 30, and it will cause a negative charge to build up on thecapacitor. If'no other signal is furnished to the capacitor 30 than thatfrom the transistor 96' in the constant current circuit 27, the chargeon the capacitor 30 will increase vwith each pulse of energy furnished-by the transistor 91. The potential on the capacitor 30 is applied overa lead 107 to thebase of a transistor 110 in the isolating cirv cuit 35.The transistor 110 is connected as an emitterfollower such that thenegative potential being applied to the base thereof appears on theemitter and rend-ers a diode 111 conductive so that this decreasedpotential appears acrossa resistor 112. The voltage across the resistor112 is applied to the base of a normally-conductive transistor 115 inthe -6 level sensing circuit 36'. When the voltage on the capacitor 30and, hence, on the base of the transistor 115 exceeds `-6 volts, thetransistor 1.15 is rendered nonconductive, and the collector potentialthereof will increase'. It can be seen, that leading transitions in thesignal on the input leads 10--10 must persist for a predetermined timeto provide suicient negative pulses 4from the retard univi-b-rator 26 todischarge the capacitor 3i) to -6 volts. When this charging potentialfor the capacitor persists for this predetermined time, for example, 2()milliseconds, the charge on the capacitor 30 and the potential of theemitter .of the transistor 110 will cause the transistor-115- in the -6volt level sensing circuit 36 to be rendered nonconductive so that apositive potential appears on its collector.

The positive potential appearing" on the collector of the transistor11S', upon its being rendered nonconduc-tive, renders a diode 116`conductive and is applied to the base of a left-hand, normallyconductive transistor 117 inthe retard liiip-iiop circuit 37. Thepositive-potential on the base of the transistor 117 renders thistransistor nonconductive, and the collector potential thereof decreases.This decreasedy potential is applied across resistors 120 and 121 to thebase of a right-hand transistor 122 in the retard flip-dop 3-7, torender the transistor 122 con- ,ductivre; The negative potential on thecollector of the transistor 117, upon its being rendered nonconductive,is

' also impressed on a lead 125 and a diode 126, but it fbeing appliedtothe lead 127V is blocked by a diode 132 so W Vthat it is 'ineiective'Howeven the positive-going transition thereof is suilicient to againrender` Ythe conducting transistor'122 noncondu'ctive toreturn theretard ilipop `37 to-thecondition`ishown in FIG. 4, that is, with theleft-hand transistor 117 conducting. When the transistor 117 againconducts, its collector potential increases,

and this increase in'potential is applied over 4the lead :125 to renderthe diode 126 conductive. Consequently, this positive potential isapplied over a lead 135 and to `the base of a normally-conducting,right-hand transistor 136 in the subtract ygate univibrator 40. Thisunivibrator is connected as a monostable flip-flop, and the positiveypotential applied to the Ibase of: the right-hand transistor .136 issutiicient to render this transistor nonconductive.

Consequently, a left-hand transistor 137 inthe univii brator `40 isrendered conductive, and such conduction jwillV be maintained for apredetermined time as determined by lthe circuittirning elements, acapacitor 140 and theresistors V141 and 142, of the univibrator.Duringthe ktime that the univibrator 40` is in its unstable state, thecollector of Ithe nonconducting transistor 136 'is at some decreasedpotential. When the univibrator -40 returns to its-'originalV quiescentcondition, thecol- .lector potential of -the transistor 136 is'V at arelatively `positive potential. These potentials areapplied to thesubtractV gate 41 over a leady1`45.

As described hereinabove, theioutput of a binary such `as the binary-147in FIG. 5 of Hansen patentV is applied to the subtract gate 41 rover alead 146. Normally, when -the subtract gate univibrator40 is in itsquiescent condition, .with theright-hand transistor 136 therein conduct-`ing, the collector of the transistor 136 is at someVrelatively-positive value which is applied over the lead'145 and whichrenders a diode 147 in the and gate 41 conductive. Under this quiescentcondition, the potential being applied at this time to the base of atransistor 150 in the or gate circuit 42 may be in the order of +1 volt,

Vand the emitter of the transistor 150 may be connected :over a lead 151to +l.5 volts. Consequently, the baseto-emitterpotentialof thetransistor 150 is negative, and

the transistor will be maintained conductive. The output of the binary(similar to the binary 147 in the HansenY patent) being applied to thelead 146 in a square Waver form and is differentiated by a capacitor 152and aV resistor 155. 'The positive spikes' resulting from Vsuch dii'-ferentiation increase the conduction of the diode 147 and drivethepotential of the base of the transistor 150 positive with respect toits emitter potential so that the ,transistor 150 is renderednonconductive. In the nonconductive condition, the collector voltage ofthe transistor 150 will decrease, and this vdecreased potential isapplied over a lead `156 to the base ofa transistor 157 in the isolatingcircuit 45 rendering the transistor 157 conductive. VThe positivespikewhich renders the transistor 157 conductive causes a positive spikeof potential to appear on the collector of the transistor 157, and sucha positive pulse is applied to the driving means of one of the frequencydividers (similar to the frequency divider 67 in Hansen Y patent) whichcauses the driving of the distributor in the receiver.

When the subtract gate univibrator 40 operates, a negative pulse isobtained from the collector of the transistor 136 in the mannerdescribed hereinabove. This-negative pulse is applied over the lead 145and to the diode 147,

and prevents the diode 147 from conducting. Under this condition, when apositive spike is furnished from the binary similar to the binary 147 inHansen patent and over thev lead 146, Athe spike is not suicient torender the diode 147 conductive so that the transistor 150 will not becut oi. This effectively eliminates one positive spike from the outputof the transistor 157 and eliminates one drive pulse for the.distributor driving means. Consequently, the distributor will be sloweddown, and this is precisely the desired result to eiect synchronirationvbetween the distributor-and the incoming signal transitions because suchtransitions Werelagging the distributor as Vdescribed hereinabove.. f

Each timevthat the -6 volt level sensing circuit 36 operates, a drivepulse is eliminated from the distributordriving meansin the mannerdescribed hereinabove. This occurs sincerthe rendering nonconductive ofthe transistor 115 in the -6 volt level sensing circuit operates theretard dip-flop circuit 37. When this latter circuit operates, theleft-hand, normally conductive transistor 117 thereinV is renderednonconductive, and the collectorppotential thereof drops. This drop inpotential is impressed Von a lead 160 and causes the voltage at ajunction point 161 to become negative. This negative potential is thenapplied Yto the base ofa normally-nonconductive transistor 162 in theretard discharge circuit 47, to render the transistor 162 conductive.When the transistor 162 conducts, there is current flow from ground,throughthe transistor 162, a diode 165, a resistor 166, the vresistor1&5 and the capacitor to -12 v. This current ow tends to produce a zeropotential at a junction point 167 and' Y will cause aV reduction in thenegative charge on the capacitor 30. Thereafter, when the transistorv117 is rendered conductive, .upon the retard flip-liep 37 returning toits original state, the collector potential thereof increases,

.and such an increase in potential is applied over the lead `160 andagain renders the transistor 162 nonconductive. With this structure thenegative charge which had built up on the capacitor 30 is made morepositive. It the lagging condition of the input signal continues,negative increments of potential continue to be built up on thecapacitor30 until it reaches -6 volts. At this time, the transistor V115 in the-6 volt level sensing circuit 36 is again rendered nonconductive, andanother pulse is deleted from the distributor driving means.Consequently the voltage to which the charge on the capacitor 30 isbuilt by the retard discharge circuit determines the maxivvolts, atransistor 180 in the +6 volt level sensing circuit 51 is .renderednonconductive.

mum rate at `which pulses are deleted from the distributor-drivingmeans'. Y Y

Substantially the same structure is provided for adding drive pulses tothe distributor-driving means in the cases where theincoming signalleads the receiver distributor and such a leading condition persists fora predetermined time. In this latter situation, stages similar to theVstages 161e to 191g, inclusive, ofthe Hansen patent, apply outputs toVthe base `of a transistor 170'in .the amplier 25, rendering thetransistor conductive. As describedhereinabove, when a clock pulse isapplied to the lead 115, the advance univibrator 31 will be operated,and the conductive states of two transistors 171 and 172 therein arereversed from'that shown in FIG. 2 for -a predetermined time. An outputfrom the advance univibrator is applied to alead 175l and to the base ofa transistor 176 in the Vconstant current circuit 32. Consequently, thecapacitor of the constant current circuit 32'is also appliedto the baseof' a transistor 17-'7 in the isolating circuit 5G, and when it, reachesva potential slightly greater than +6 An output, taken from thecollector of the transistor renders a transistor 181 in the phaseinverter circuit 52 nonconductive, and an output therefrom operates theadvance dip-flop 55 in a manner similar to the operation of the retardilipop 37. Thereafter, the add gate univibrator 56is operated so that aleft-hand, normally nonconductive transistor 182 therein is renderedconductive for a predetermined time. When the transistor 182 is renderedconductive, the collector potential thereof increases, and the increasedpotential is impressed over a lead 183. Prior to this time, that is,when the transistor 182 was nonconductive, the relatively-negativepotential on the collector thereof prevented the conduction of a diode185 in the and gate circuit S7.k Under this condition, the diode 185could not be rendered conductive bythe output from the binary in thefrequency divider of the distributordriving means. As mentionedhereinabove, this binary is similar -to the binary 189 of the Hansenpatent, and its square wave output is applied to a lead 1-86, isdilferentiated by a capacitorY 187 and the resistor 155, and thepositive and negative spikes resulting from such differentiation arelapplied to the diode 185. The positive spikes are not suflicient toovercome the negative potential being applied to the diode 185 from thecollector of the nonconducting transistor 181 in the add gateunivibrator 56. When, however, the add gate univibrator 56 is operatedand the transistor 181 therein is rendered conductive, the positivepotential on the collector o fvthis transistor is applied through thediode 185 and tothe base of the normally conducting transistorY 150 inthe or gate 42.

to the emitter of the transistor 150, this transistor will remain in itsconductive condition. During the time that the diode 185 is conducting,a positive spike is furnished from the binary (similar to the binary 187in Hansen patent) to the lead 186, and this positive spike is alsoapplied to the diode 185 and to the base of the conducting transistor159. In this case, suicient positive potential is applied to the base ofthe transistor 150 to render the transistor nonconductive. Consequently,the collector potential of the transistor 150 decreases, andthisdecreased potential is applied over the lead 156 and to the base ofthe normally-nonconducting transistor 157 to-render this transistorconductive. When the transistor `157 is rendered conductive, a positivespike appears on the collector thereof. Since the signals being appliedto,

the capacitor 187 are 180 degrees out of phase with each other, when theadd gate univibrator 56 operates, one extra spike appears in the outputpotential at the collector of the transistor 181. This additional pulseis applied to the distributor-driving means to speedup the operation ofthe receiver distributor. It can be seen that this was the desiredresult since the signals being applied to the input leads 10-10 wereleading the distributor, and the distributor had to bespeeded up inorder to cause synchronization therebetween.

Each time the advance flip-flop 55 is operated to add a pulse to thedistributor driving means, aA portion of the positive charge on thecapacitor 30 is removed therefrom by the advance discharge circuit 69.When the advance flip-op 55 operates, a right-hand transistor 190therein is rendered conductive, and the collector potential thereofincreases. This increased potential is applied over a lead `191 and tothe base of a transistor 192 in the advance discharge circuit `60 torender the transistor -192 conductive. When the transistor-,192conducts, there is current ow from ground, through ther-meter movement102, the resistor 105, a resistor 195, a diode 196 and the transistor192 to ground. This current flow tends to produce a negative voltage atthe junction point 167 and will cause a reduction in the positive chargeon the capacitor 30. When the transistor 190 is rendered nonconductiveagain, after a cycle of operation of the advance flip-hop 55, itscollector potential drops, and this drop in .potential is applied overthe lead 19.1 and to the base of the transistor 192 in the advancedischarge circuit 60, rendering the transistor 192 againy nonconductive.The circuitry is so designed that a portion of the f However, in view ofthepositive potential being applied FIG. 6a shows a plurality of voltagespikes that represent outputs from the constant current circuit 32 whichisl energized by the advance univibrator 31. The plurality of voltagespikes shown in FIG. 6b represents the output from the constant currentcircuit 27 which is operated by the retard univibrator 26. As describedhereinabove, the effect of multipath transmission on the incomingsignals will be to cause transitions therein to both lead and lag thereceiving distributor. Also, should a given transition vary about itsoptimum position, it is possible to have inputs to the amplifiers 22 and25 at substantially the same time. In this case, the' advanceunivibrator r31 and' the retard univibrator 26 will be operatedV atsubstantially the same time so that equal positive and negative chargingimpulses are applied to the capacitor 3 0.' When this occurs, there isno net effect on the charge onthe capacitor 30. This and-otheroperations of the circuit can be seen by referring to FIG. 6c, whereinv.a'n exaggerated representation ofthe charge on the capacitor 39'isshown. V

Referring to FIG. 6c, assume that the circuit is established at timevt1. Y At this time, it can be seen by referring to FIG. 6a, that theinput signals vare `leading the receiving distributor so that onlypulses are received from the advance sidev of the synchronizer. Thesevoltage spikes place a positive-'going charge on thev capacitor 30, andwhen such a charge reaches +6 volts (at time t2) a pulse is added tothedistributor-driving means as shown at point 200 in HG. 6d. 'I'he advancedischarge circuit 60 dischargesA the capacitor Sti to a point ,201 (FIG.6c), but

since the incoming signal continues to lead the receiving distributor,pulses on the advance side again charge the capacitor30 to +6 volts.Each time this occurs, a pulse is added to the distributordriving means,as can be seen the times t3 and t4).

in FIG. v6d between times'rz and t3v Between times t3 and t4, pulses areAgenerated on both the advance andretard sides, but referring to FIG. 6aand 6b; it can be seen that more pulses occur on the advance side thanon the retard side. Conscquently,.when` pulses are actually generated atthe same time on both sides, there is substantially no elfect on thecapacitor 3d (see'FIG. 6c between When, however, no pulses occur on theretard side, the capacitor 30 is charged to its +6 volt potential sothat an additional pulse is applied to the distributor-driving means.

Between the times t4 and t5, a series of pulses' first occurs on theretard side, and then a series of pulses occurs on the advance side.Consequently, during this time interval, the capacitor 30 ischargednegatively, and, when the pulses occur on the advance side, thecapacitor is charged in a positive direction. At t5, a long series ofpulses starts only on the retard side. Consequently, the capacitor ischarged negatively, and when such charge reaches -6 volts, the retardflip-flop 37 is actuated-to remove a pul'sefrom thedistributor-drivingmeans. This occurs at the point 202 shown in FIG. 6d. Since the pulsespersist lon the retard side during thel interval between times t5 andf6, two further pulses are removed from the distributor-driving means,and these removals are designated bythe points 265 and 2016 in FIG. 6d.

Then, attime te, multipath transmission has caused the signal to' leadthe' receiving distributor so'y that pulses are received only on theadvance side. These pulses cause the capacitor to be charged in apositive direction until the charge thereon is -l-'6 volts. At thistime, the time t7, a pulse is addedv to the distributor drivingme'ansbecause of the persistence ofthe leadiug condition ofthe signal withrespectto the receiving distributor. During .time t7 to t8, furtherpulses occur only on the advance side so thata plurality of pulses areadded to the distributordriving means. l'Then between times f8 and r9,the ,re- 'ceiving distributor is in substantial synchronism with theincoming signals so that pulses apply on both the advance and.` retardsides; When pulses occur on both sides, there i .is nosubstantial eecton the capacitor 30', the usual vol*- age leakage from the capacitor isrep/resentedV by that por- .tion of the curve identied by referencenumeral 2;@3. v

y When, however, moreY pulses occur on the advance side than on theretard side, drive pulses are` eventually added to thedistributor-driving means.

From the above description, it can be seen that the eiiect I ofmultipath transmission on the synchronizer embodying the invention isaveraged out for all practical purposes.

In the overall picture, the result of multipath transmission can `beseen by referring to the capacitor. potential in FIG. 6c during theinterval between times t4 and t5 There, .the capacitor 30 is lirstcharged ina negative direction, ,then chargedV in a positivedirection,and nally, again charged in the negative direction. During this wholetime,

distributor-driving means. This result is desirable since, in theoverall picture, multipath transmission will usually average out. Withthe present invention, such averaging out'is caused by not permittingthe synchronizer either to add pulses'to or to subtract pulses from thedistributordrivingrrneans unless the leading orvlagging of the'in-.coming signal with respect to the distributor persists until apredetermined charge on the capacitor has been accumulated. Y

Alternate Embodment -ln this alternate erncircuit 236 is energized tosubtract drive pulses from the Vdistributor driving meansasexplainedwith reference to i, Y FIG. l. Also, the capacitor 330`isicharged through' a constant current circuit 232 until a +6 volt levelsensing circuit 251 is energized thereby to cause, eventually, the

' addition of a drivepulse to the distributor driving means.

A meter movement 302 is connected across the capacitors A230 and 330 tomeasure the differential charge therebetween.

Frequency Synchronization l In multiplex equipment, asin all electricalsystems having'aplurality of variables, the greater the number ofVariables which can be controlled, the greater the overall controlfwhich canbe exercised over therequipment or systems. The foregoing hasdealt with the control of the phase relationship between, the signalsreceived by Va Qmultiplex receiver and the signals produced by the localoscillator of the multiplex receiver. If, in addition to independentmeans for controlling the phase relationship of the signals, means areprovided for controlling the frequency of the local oscillator at boththe transmitter and receiver multiplexes, analogous to oscillator 66'disclosed in the above-identified Hansen patent, a higherdegree ofmultiplex andthe receiver multiplex.

no pulses have been either added to or subtracted from the 'vi 523having separate. windings 324 and 32s. YThe lrotative device .323 is ofthe dual `rotative type disclosed and power amplifiers 308 and 318,respectively. Amplilir circuit 391 is'connected, `as indicated 'byterminal 302, to the collector of transistor 122 of retard flip-flop 37,FIG, fl, and ampliiier circuit 311, as indicated by terminal 312, isconnected to the collector of transistor 19o of advance ilip-op 55.

Upon theindication of a phase displacement between the locally producedsignals and the received signals, ktor example, a `lead inV phaserelation, the retard flip-flop 37 is triggered to itsl second state,with the right-hand side conducting, and transistor 122V is driven tosaturationland remains at saturationiuntil the flip-flop 37 is yreset'by pulse from the Achannel clock over the lead 127'.v Astransistor 122Vis driven to saturation, its collector potential rises and this riseis'coupled to the baseof emitter iol# lower 364 of the ampliiier'circuit301. As the base of emitter follower 3My rises in potential, thepotentialof the emitter follows correspondingly and the rise inpotential is coupled to the base of amplier transistor 306 by resistor393, and is of sutiicient magnitude to render transistor 306 conductiveto a state of saturation. As transistor 3% is driven to a state ofsaturation, its collector `becomes increasingly `negative andtbis'negative-rise is coupled by resistor 305 tothe fbasejof power-transistor34108 and renders the transistor 398 conductive to a state ofsaturation. When transistor 308 is conducting to a statevof saturation,an energization circuit is completed from' the source of potential V31%,through the rotative device winding 324 and through thecollector-emitter circuit of-transistor 393 to ground.V Thus therotative de- Y vice is` energized andits shaft 36S is rotated apredeterlsynchronization can be eected between the transmitterAccordingly, there are shownrin FIG. 8, two amplifier circuits, '301 and311, operable to adjust the frequency of Vthe local oscillator 320 inaccordance with the phase able capacitor 321 which is controlled by arotative deacross the oscillator 320 is a tank vcircuit, including avarimined amount and in such'a directionas to increase the .capacitanceof -capacitor 321 and accordingly, decrease the frequency ofthe crystaloscillator 32.0.

In similar manner, amplifier circuit 311 isv operable to v elect adecrease in the capacitance of capacitor 321 and hence increase'tliefrequency of the oscillator 320 upon the indication of a lag in phaserelation in the phase synchronization circuitry. Transistor 190, o fadvance flip-flop 55, is driven to saturation upon the indication of aretard phase condition between the received and transmitted signals, andis eective to turn on emitter follower 314. The operation of emitterfollower 314 renders Vampliier 316 conductive to saturation andconsequently, renders amplifier' 318 conductive to a state ofsaturation. When transistor 318 is conducting to saturation, anenergization circuit is completed from rthe source of potential 310,Vthrough the winding-'.325 and the collector-emitter circuit oftransistorr318. Consequently, the rotative device 3231is actuatedand-the shaft. 309 is rotated in such a direction as to-decrease thecapacitance of variable capacitor 321 apredetermined amount and hence toincrease the frequency ofthe local oscillator 320. Thus the rotativedevice controlled capacitor 321 operates as a vernier for obtaining finecontrol over the receiver multiplex and for obtaining a lhigh degree ofsynchronism fbetween the oscillators of the transmitter and receivermultiplexes. l

Each multiplex station is provided with the two ampliiier circuitsforcontrolling the local oscillator and, since the local oscillator at eachmultiplex station pulses both the transmitter and receiver multiplex,the local oscillators will be chasing each other. Accordingly, an exi3tremely high degree of frequency synchronization is achievedbetween thelocal oscillators of the multiplex stations.

It` will be understood that the frequency control circuitry of FIG. 8 isdesignedV for integral operation with both the preferred andalternate'embodiments of applicants invention. Also, the frequencycontrol circuit may be cut out, lby suitable switching means, of themultiplex system and themultiplex system operated with only the phasecorrection circuitry utilized.

it is to be understood that the above-described arrangements andconstruction of elements are simply illustrative of the invention andmany 'other modiiications may be made Without ydeparting from theinvention.

What is claimed is:

l. A telegraph receiver synchronizer which comprises means yfor sensinga leading transition in a telegraph signal, means for sensing a laggingtransition in the telegraph signal, a single synchronizing informationstorage capacitor, means energized by the two sensing means for applyingto said one capacitor incremental charges of positive or negativepolarity depending upon which of said two sensing means senses atransition, and utilization means enerm'zable by the capacitor uponaccumulation thereon of a positive or negative charge of predeterminedmagnitude relative to a standard potential for imposing a correctiveeffect on telegraph receiver.

2. A telegraph receiver synchronizer which comprises means for sensingtransitions in a telegraph signal including transitions which occur atother than an optimum time, a single synchronizing information storagecapacitor, means energized by the transition sensing means for applyingcumulative charges on said one capacitor, and utilization meansenergized by the stored charge on said one capacitor upon accumulationthereon of a charge equaling a predetermined magnitude in response tothe occurrence of transitions at other than optimum time for imposing acorrective effect on the telegraph receiver.

3. A telegraph receiver synchronizer which comprises means for sensingthe transitions in a telegraph signal, a single synchronizinginformation storage capacitor, means energized by thetransitions-sensing means for applying incremental charges on said onecapacitor of positive or negative polarity utilization energized by thecharge on said one capacitor upon the accumulation thereon of a chargeat least .equaling a predetermined positive or negative potential, andpositive and negative discharge circuits for partially reducing thecharge on the said one capacitor each time one of the utiiization meansis energized thereby.

4. Apparatus for synchronizing the distributor of a telegraph receiverwith a received signal, which comprises means for comparing times ofoccurrence of transitions in the received signal with the times ofoccurrence of transitions as predicted by the receivingk distributor, asingle synchronizing information storage capacitor, means energized bythe signal-transitions-comparin'g means for incrementally charging andoppositely charging said one capacitor in accordance with the signaltransitions occurring atV times other than optimum times, and meansenergized only upon accumulation of a predetermined charge on said onecapacitor for correcting the phase relationship of the distributor toreceived signals.

5. Apparatus for synchronizing a telegraph receiving distributor withthe signals received thereby, which comprises sensing means forproviding a control pulse each y i4 reaching a predetermined chargedcondition-and in a second sense upon the same capacitor 'reaching' apredetermined diiierent charged condition, and means operatedby thecorrecting means' for varying the speed of the receiving distributoruntil the locally generated timing pulses coincide with the time ofoccurrence of the signal transitions. Y' l 6. Apparatus forsynchronizing a telegraph receiving distributor 4with telegraph signalsbeingreceived thereby, which comprises Aa first sensing meansforsensing` transitions in the signals which occur before a predeterminedoptimum time, a second sensing means for sensing transitions in thesignals which occur after the optimum time, a

single synchronizing information storage capacitor, a firstA constantcurrent circuit for impressing `equal incremental charges on said onecapacitor, a second constant current circuit for impressing'equalincremental charges of opposite polarity on said one capacitor, meansoperated by each of the sensing means for energizing one of the constantcurrent circuits and for placing its incremental charge on said onecapacitor, and utilization means energized by the accumulation on saidone capacitor of a charge of a predetermined magnitude and of eitherpolarity for correspondingly varying'the speedofl the receivin-gdistributor. Y

7. Apparatus for synchronizing the distributorofa receiver of telegraphsignals with the transitions-of the received signals, which comprisesiirst sensingmeans for generating a pulse of predetermined duration eachtime "a transition in the received signal occurs beforean' optimum timeas determined by the receiving distributor, second sensingmeansforgenerating a pulse of predetermined duration each time a transitioninthe' receivedsignal occurs after the optimum time, singleV synchronizing'information storage capacitor, a first charging circuit ,energized bysaid one rst sensing means forcha'rging the capacitor an incrementalamount proportional to the pulse duration each time a pulse is generatedby the first sensing means, a second charging' circuit energizedby thesecond sensing means for oppositely charging said one capacitor anincremental amount proportional to.

the pulse duration each timea pulse is generated by the second.fsensingmeans, a rst llevel sensing circuit, ener- 8. 'In a telegraph receiverincluding a local oscillator `and a distributor, apparatus forsynchronizing the receiver withsignals received from a telegraphtransmitter, which comprises a gate circuit interconnected between thelocal oscillator and the distributor, lfirst sensing means Vforgenerating a pulse of predetermined duration each time -a transition inthe received signal occurs before an optimum time as determined bytiming pnl-ses produced by the local oscillator and applied to thedistributor through said gate circuit, second sensing means forgenerating a pulse of predetermined duration each time a transition inthe received signal occurs after the optimum time, single synchronizinginformation storage capacitor, a iirst charging circuit energized by thetirst sensing means rfor charging said one capacitor an incrementalamount proportional to the pulse duration each time a pulse is generatedby the tirst sensing means, a second charging circuit energized by thesecond sensing means for oppositely charging said one capacitor anincremental amount proportional to the pulse duration each time a pulseis generated by the second sensing means, a trst level sensing circuit,energized by said one capacitor upon reaching a predetermined charge, asecond level sensing circuit energized by said Y 15 one capacitor upon.reaching a predetermined opposite charge, means operated by the' twolevel sensing circuits for adding or withholding pulses from the pulsespassed by said gate dependent upon the energization of one or Y theother of the level sensing vcircuits, and motor controlled capacitivemeans for increasing or decreasing the frequency of the local oscillatordependent' upon the energization of oneY 'or' the other of the levelsensing circuits. Y

"97. In a telegraphreceiver having a local oscillator for controllingits operation, apparatus lfor synchronizing the frequency oj the localoscillator with received signals upon occurrence of -a phasediierentialbetween the receivecl signal transitions and the pulsesproduced by the local oscillatonwhich comprises,V a tank circuitconnected across the local oscillatorincluding a variable capacitor, arotativev device forvarying the capacitance of said capacitor, meansincluding an energizable Winding for rotating said device in onedirection, means including another I en'ergi'z-able winding Iforrotating said device in the otherV direction, means for sensing a lag inphase relationship vbetween the locally produced .pulses and receivedsignal transitionsfand operable to produce an output pulse of i onepolarity to indicate occurrence of a phase lag, means cumulatd on saidone capacitor as representing a phase lagging condition, arst amplifiercircuit foramplifying the output of said first voltageA sensitivecircuit and lfor eiectinglenergization of one of -sa-id rotative devicewind- Aiugs-todecrease the capacitance of said variable capacitorandtherebyrto' increase the frequency of the local oscilvlator, and asecond ampliercircuit for amplityingthe i output of saidsecond voltagesensitive Ycircuit andV for efinfecting` energization of the other ofsaid rotative device windings `to increase the capacitance of thevariable capacitor and thereby to decreaserthe frequency of the localoscillator. n A

V10. In a telegraph receiver having a local oscillator forcontrolling'its operation and anfrequency divider network operabletherefrom, apparatus yfor synchronizing the frequency of the localoscillator with received signals upon occurrence of an out-of-phaserelationship of the received signal transitions tothe frequency dividertransitions derived from the local oscillator comprising rst means forgenerating a control .pulse to indicate occurrence of a ,leading phaserelationship between the locally produced transitions and the receivedsignal transitions, means operable by saidrrst control pulse generatingmeans to Withhold pulses from the frequency divider network and simulltaneously to decrease the frequency of the local oscillator, sewnd meansfor generating a control pulse to indicate occurrence of a lagging phaserelationship between the locally producedV transitions and the receivedsignal transitions, and means operable by said second control pulse.

generating means to add pulses to the frequency divider network andsimultaneously to increase the `frequency' of the local oscillator, andmeans for disabling only the local oscillator frequency correctionmeans. s

ll. Ina telegraph receiver having a local oscillator for controllingVits operation and a frequencydivider network operable'therefrom,apparatus ,for synchronizing the frequencyfof the local oscillator withreceived signals upon occurrence of an out-of-phase relationship of thereceived signal transitions to the frequency divider transitions derivedfrom the local oscillator comprising a first gating circuit fordetecting a leading phase relationship between Y locally producedtransitions and received signal transitionsywhich when detected initiatea control pulse, a

signal synchronizer information storage capacitor, means activated bysaid control pulse for placing a positive charge Yof predeterminedduration upon said capacitor, a second gating circuit for detecting alagging phase relationship between locally produced transitions andreceived signal transitions which Whenrdetected initiate a controlpulse, means activated by said second-mentioned control pulse forplacing a negative charge of predetermined duration upon theV samesingle synchronizer information storage capacitor, sensing meansenergized in a rst sense under the control of said one capacitor uponaccumulation thereon of a predetermined charge and in a second senseunder the control of said same capacitor upon accumulation thereonof apredetermined different charge, a first partial discharging meansoperated by said yiirst sensing means upon sensing the Erst-mentionedpredetermined Y charge, a second partial discharging means operated bysaid second sensing means upon sensing the predetermined diierentcharge,'a variable capacitor for varying the frequency of the localoscillator, arrotative device for controlling said variable capacitor, afirst frequency correction circuit activated by said iirst sensing meansfor energizing the rotative device to increase the capacitance of thevariable capacitor and thereby to decrease the frequency of -the localoscillator, a second frequency correction circuit activated Iby saidsecond sensing means for energizing the rotative device oppositely fordecreasing the capacitance of the variable capacitor to increase thefrequency of the local oscillator, and a` correction means operatedsimultaneously with the frequency correction means and initiated by thetwo sensing circuits, respectively, for adding or Withholding pulsesfrom the frequency divider Vnetwork upon energizat-ion of oneV or theother of said ensing means.

VReferences Cited in the le of this patent UNITED SLYIESV PATENTSVGriflith Nov. 13, 1951 Hansen May 6, 1952

